According to Hoekstra et al. (2011) the water footprint within a geographic area is defined as the total freshwater consumption and pollution within the boundaries of the area. The grey part of the water footprint refers to pollution and is an indicator of the water volume needed to assimilate a pollutant load that reaches a water body. It is possible then, based on the grey water footprint to estimate if the water available in a river at a particular crosssection will be sufficient to maintain a water pollution level (WPL) below 100%. The crossing of 100% indicates that the waste assimilation capacity has been fully consumed in this particular catchment. In this paper, the grey water footprint from nonpoint source pollution has been calculated based on long-term hydrometrological data for the upper part of a small agricultural catchment (area of 23.4 km2) (Zagożdżonka River) in central Poland. Based on land use and the amount of fertilizers applied in the catchment, together with information about the natural concentration of nitrogen and phosphorus in the river, as well as maximum acceptable concentration, the water pollution level has been calculated for actual conditions. The estimation of future runoff decreases for the considered catchment (Banasik, Hejduk 2012) has been applied in order to estimate potential future water pollution levels. The calculation shows that, even when the management practices in this catchment remain as they are, including the current extensive crop production, the WPL of 100% will be exceeded in the year 2033 (for phosphorus) and 2043 (for nitrogen) due only to the decreasing availability of water.